Two-way radio communication systems that geographically reuse carrier frequencies that are used to support two-way communications are well known in the art and include, for example, cellular radio telephone systems. Other two-way communication systems, such as the SmartZone multisite trunked land mobile dispatch systems offered by Motorola, Inc., also make use of geographic reuse of transmit and receive frequencies.
Typically, reuse occurs pursuant to a reuse pattern; for example, both 7 cell and 4 cell reuse patterns are known in cellular telecommunications, as are other patterns. Such reuse patterns are typically based on a model representing ordinary (or perhaps worst case) use of such a system. Once selected, however, a particular model, and the system implementation based thereon, does not typically allow dynamic reorientation of the geographic reuse pattern or plan in response to varying system conditions; in particular, such reuse patterns represent a compromise, and therefore occasionally provide either too much or inadequate buffer zones between areas of frequency reuse during actual use.
The applicant has determined that the type of communication unit operating on an allocated frequency can have significant impact on the efficiency and/or protection offered by a particular reuse strategy. With reference to FIG. 1, a portable communication unit will typically have a relatively small effective coverage area (101), due to power limitations, antenna effectiveness, and so forth. A land vehicle mounted communication unit will, on the other hand, typically have a larger effective coverage area (102), due to typically increased power capabilities, better antenna structures and orientation, and the like. An airborne communication unit can exhibit an even greater increase in coverage area (103) due substantially to improved antenna placement.
With the above in mind, a fixed frequency reuse plan may make inefficient use at any given moment of available frequencies by providing too large a buffer zone when portable communication units are being supported, and similarly may allow interfering instances of reuse when accommodating an airborne communication unit.
Accordingly, the applicant has determined that a need exists for a methodology for dynamically altering frequency reuse patterns to accommodate differing communication unit types.